Amplifying with vacuum tubes



, Patented May 13, i924.

mural) STATES teases PATENT orrlca.

DAVID G. BLATTNER I, OF BOGOTA, NEW JERSEY, ASSIGNOR T0 WESTERN ELECTRIC COMPANY, INCORPARTED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

AMPLIFYING WIlITH- VACUUM TUBES.

Application filed June a,

To all whom it may cOme-rn:

Be it known that 1, DAVID G. BLATTNER, a citizen of the United States, residing at Bogota, in the county of Bergen, State of rom a common source is supplied, through parallel paths, to the push pull stage and to a preceding stage. Other and further objects'will be apparent from the detailed description hereinafter ofthe accompanying drawing.

- In accordance with the invention as applied to the type of push-pull tandem amplifier circuit mentioned above, a filter is inserted in at least one'of the parallel paths or connections from the common space cur rent source to the amplifier stages, in order to prevent the feeding back of electromotive force waves from the output side of the push-pull stage to its input side through the connections for supplying space current. i

The accompanying drawing is a diagram of an amplifier circuit embodying the preferred form of the invention. I

In the drawing current is supplied from line 1 to line 2, through a multi-stage amplifier circuit, the first stage comprising a vacuum tube 5 and the second stage being a push-pull amplifier comprising vacuum tubes 7 and 9. The two stages arecoupled by means of the transformer 11. lhe pushpull stage is coupled to line .2 by means of a transformer 12. I

The filaments ofall of the tubes are heated by alternatin cmrent from the generator A in accor ancewith the principles set forth in United States patent application of R. A. Heising, Serial Ho. 124,953, filed October 11, 1.91.6,- entitled Circuit connections of electron discharge apparahas new Patent No. 1,432,022,. granted Go- 1921. Serial No. 474,891.

tober 17, 1922. Obviously, any other suitable cathode-heating means, as for instance, a direct current source, might be used.

Space current for all of the tubes is supplied from the common source B, the plate circuits of all of the tubes being connected- 'in parallel to each other with respect to the source B. Thus the space current for the tube 5 passes from battery B, through lead '13, primary winding of transformer 11, to the anode of the tube, through the tube to the cathode, and through leads d in parallel, the upper and lowerhalves of impedance 6 in parallel, leads 15, 17, 19 and 21 back to battery. The s ace-current for tube 7 .passes from battery through lead 23-, the upper half of the primary winding of transformer 12, to the anode, ofthe tube, through the tube to the cathode, through leads 8 in parallel, the upper and lower halves of impedance 10 in parallel, and lead 25, back to the battery. The space current for tube 9 passes from battery B through lead 23,'thc lower'half of the primary winding of transformer 12, through the tube, through leads 8 in parallel, through the two halves of impedance 10 in parallel, and through lead 25, back to the battery. Each half of impedance 6, and

each half of impedance 10 may consist of a 100 ohm resistance, for instance.

Although the upper and lower halves of the push-pull circuit comprising amplifiers 7 and 9.are generally regarded as balancing i each other so that there is substantially no alternating electromotive force between 1 leads 23 and 25,.it has been found that in some cases a considerable alternating elec tromotive force exists between these leads,

especially where the impedance between anode and cathode is not the same in the two tubes 7 and 9. This electromotive force causes a considerable amount of alternating current toflow through these leads and the battery B, since the leads co-ntaincno choke coils or other elements of high impedance to current of the frequency of the current being transmitted through the amplifier. Thus, an alternating electromotive force ice equal to the drop produced inbattery B r by the alternating current therein ap plied to leads 13 and 21, and therefore in accordance with this invention, means are provided to prevent this electromotive force from sending current waves through the primary winding of transformer 11, and

thereby efi'ectin the in ut circuit of the g} P also affords a path of low impedance between leads 27 and 29 for any current waves transmitted to these leads from the juncture of leads 23 and 25 with leads '13 'and 21 respectively. Choke coils 27 and 29 tend to prevent the transmission of any current.

waves through leads 13 and 21. Thus, the

' feeding back of alternating current from the output side ofthe push-pull amplifier stage to its input side and the singing which would result from such action are prevented.

Were it not for the filter, noise or singing might arise from voltage drop in battery B due to the alternations of heating current in the filaments of the push-pull amplifier. Although the push-pullconnection tends to prevent the appearance in line-2 of current waves due to the alternations of heating currents in the filaments of the push-pull amplifier, by reason of the fact that an increase, say, in current in one half of the primary winding of transformer 12 due to a change of the instantaneous average grid-filament potential and the instantaneous average plate-filament potential in one of the tubes of the push-pul1 amplifier is accompanied by an increase in current in the other halfof the primary winding of transformer 12 due to a corresponding change of the instantan ous average grid-filament potential and the instantaneous average plate-filament potential inthis other tube, still, an increase in current in both halves of the primary winding of transformer 12means an increase of current through leads 23 and 25, and an, increase .of voltage drop in the battery B; and this increase of drop would act upon the grids of thetubes of the pushpull amplifier through transformer 11, were it not prevented from doing so by thefilter.

What is claimed is:

l. A vacuum tube amplifier comprising two amplifying tubes connected in a pushpull relation, saidtubes having input circuits and output circuits, a vacuum tube, said vacuum tube feeding each of said input circuits, a source, connectionsfor supplying space current from said source to all of said tubes in parallel, and means for preventing a feeding back of current waves from said amplifier tubes to said feeding tube through said connections.

2. A push-pull vacuum tube amplifier comprising two amplifying tubes, said amplifier having input circuits and output'circuits, a vacuum tube, said vacuum tube feeding each of said input circuits, a source, connections for supplying space current from said source to said amplifier and to said feeding tube, and a wave filter inserted in said connections and between the output side of .said amplifier and the output side of said tube, for preventing said amplifier from singing due to the transfer of energy from its output side to its input side through said connections. a

3. In combination, a push-pull electron discharge amplifier comprising control'electrodes and space current paths, an electron tube for feeding said amplifier, a transformer coupling said tube and said amplifier for impressing potentials of opposite signs simultaneously upon said control electrodes, respectively, an output transformer for said amplifier comprising a primary winding and a secondary winding, a common source of space current for said tube and said amplifier, a connection for supplyin space current'from said source to said tu e, a connection in parallel to said first mentioned connection for supplying space current from said source to one of said space current paths through one half only of said primary Winding and for sup-plying space current from said source to the other of said space current paths through the other half only of said .primary winding, one .of said connections being of low impedance for alternating current and said other connection comprising means for preventing said amplifier from singing.

4. A push-pull amplifier, a vacuum tube for feeding said amplifier, a transformer coupling said tube and said amplifier, a common source of space current for said tube and said amplifier, a connection. for supplying space current from said source to said tube, a connection in parallel to said first mentioned connection for supplying space current from said source to said amplifier, and a wave filter in one of said connections for preventing said amplifier from singing, said wave filter comprising an inductance and a capacity.

5. A system comprising a vacuum tube, a second vacuum tube for feeding the first mentioned tube, a-transformer comprising a primary winding connected to said second tube and a secondary winding connected to the first mentioned tube, for coupling said second tube to the first mentioned tube, an output transformer for said first mentioned tube comprising a primary winding and a secondary winding, a'source of space current for said tubes, connections for supplying space current from said source to said first mentioned tube through the primary windassesses ing of said output -'transformer, said connections having low impedance for alternating current, and connections for supplying space current fi'om said source to the other of said tubes through the primary winding of said coupling transformer, said last mentioned connections comprisinga choke coil impedance for alternatinghaving a high current.

6. Electric wave transmitting apparatus comprising a push-pull electron tube amplifier, said amplifier having hot cathode means and having tube input circuits and tube output circuits, an amplifying electron tube having a hot cathode, said tube feeding each of said input circuits, a common source ofspace current for sald amphfier and said tube, and a common source of cathode heatinqcurrent for said amplifier and said tube. Electric wave transmitting apparatus comprising a push-pull electron tube amplifier, said amplifier having hot cathode means and having tube input circuits and tube output circuits, an electron tube having a hot cathode, said tube feeding each of said input circuits, a common source of space current for said amplifier and said tube, and a common source for lically varying heating current to said amplifier cathode means and to said electron tube cathode.

8, Electric wave transmittingapparatus comprising a push-pull electron tube amplifier, said amplifier having hot cathode means and having tube input circuits and tube output circuits, an amplifying electron tube having a hot cathode, said tube feeding each of said input lizircuits, h

cyclica y V9. in eatin current to ai d liot cathode m d ans of sai push-pull amplifier.

supplying cyce and means for sup- In witness, whereof, I hereunto subscribe my name this 2nd dagof June, A. D. 1921.

DAVI G.--BLATTNER. 

